David A. Cremers

Laser-Induced Breakdown Spectroscopy (LIBS): History and fundamentals of LIBS

Introduction Laser-induced breakdown spectroscopy (LIBS) is a method of atomic emission spectroscopy (AES) that uses a laser-generated plasma as the hot vaporization, atomization, and excitation source. Because the plasma is formed by focused optical radiation, the method has many advantages over conventional AES techniques that use an adjacent physical device (e.g. electrodes, coils) to form the vaporization/excitation source. Foremost of these is the ability to interrogate samples in situ and remotely without any preparation. In its basic form, a LIBS measurement is carried out by forming a laser plasma on or in the sample and then collecting and spectrally analyzing the plasma light. Qualitative and quantitative analyses are carried out by monitoring emission line positions and intensities. Although the LIBS method has been in existence for 40 years, prior to 1980, interest in it centered mainly on the basic physics of plasma formation. Since then the analytical capabilities have become more evident. A few instruments based on LIBS have been developed but have not found widespread use. Recently, however, there has been renewed interest in the method for a wide range of applications. This has mainly been the result of significant technological developments in the components (lasers, spectrographs, detectors) used in LIBS instruments as well as emerging needs to perform measurements under conditions not feasible with conventional analytical techniques. A review of LIBS literature shows that the method has a detection sensitivity for many elements that is comparable to or exceeds that characteristic of other field-deployable methods.

Laser-Induced Breakdown Spectroscopy (LIBS): A New Spectrochemical Technique

We have used the breakdown spark from a focused laser beam to generate analytically useful emission spectra of minor constituents in air and other carrier gases. The medium was sampled directly. It was not necessary to reduce the sample to solution nor to introduce electrodes. The apparatus is particularly simple; a pulsed laser, spectrometer, and some method for time resolution. The latter is essential in laser-induced-breakdown spectroscopy (LIBS) because of the strong early continuum. High temperatures in the spark result in vaporization of small particles, dissociation of molecules, and excitation of atomic and ionic spectra, including species which are normally difficult to detect. In one application, we have monitored beryllium in air at concentrations below 1 μg/m3, which is below 1 ppb (w/w). In another we have monitored chlorine and fluorine atoms in real time. LIBS has the potential for real-time direct sampling of contaminants in situ.